Field of the Invention
The present invention relates to a liquid ejection head for ejecting liquid by thermal energy.
Description of the Related Art
Known liquid ejection heads for ejecting liquid such as ink from the ejection ports thereof include a type of liquid ejection head designed to eject liquid by means of thermal energy. Liquid ejection heads of this type comprise energy generating elements that generate thermal energy according to the electric signals applied to them. They produce air bubbles in the liquid contained therein by means of the generated thermal energy and eject liquid by utilizing the air bubbles.
For liquid ejection heads of this type to stably perform liquid ejecting operations, the energy generating elements they have are required to sufficiently generate heat. On the other hand, they are required to suppress the electric current (the power consumption rate) for driving the energy generating elements for the purpose of energy saving. For example, Japanese Patent Application Laid-Open No. 2002-144571 describes an arrangement for improving the energy efficiency of an energy generating element to suppress its power consumption rate by increasing the current capacity of the wiring connected to the energy generating element. FIG. 6 of the accompanying drawings is a schematic cross-sectional view of a liquid ejection head having such an arrangement.
Referring to FIG. 6, an n-type impurity region 102 is formed in a semiconductor substrate 101, which is made of silicon, and a transistor 120 is formed on the n-type impurity region 102. A first heat accumulation layer 104 and a second heat accumulation layer 105 are sequentially formed in the above-mentioned order on a region of the semiconductor substrate 101 other than the region where the transistor 120 is formed. Additionally, first, second and third layer insulating films 106, 107a and 107b are sequentially formed in the above-mentioned order on the second heat accumulation layer 105 and a heater layer 109, which is to be used to operate as energy generating element 150, is formed thereon. A protection layer 115 is formed on the third layer insulating film 107b so as to cover the energy generating element 150. A dry film 114 and an orifice plate 113 are sequentially formed on the protection layer 115 in the above-mentioned order. A bubbling chamber 160 and a flow path (not illustrated) are formed in the dry film 114 at a position that corresponds to the energy generating element 150, while an ejection port 112 is formed in the orifice plate 113 so as to communicate with the bubbling chamber 160.
A first wiring layer 108a, a first via 110a, a second wiring layer 108b, a second via 110b, a third wiring layer 108c and a third via 110c are formed in the layer insulating films 106, 107a and 107b and electrically connected to each other. The energy generating element 150 is electrically connected to the transistor 120, which operates as a drive element, by way of these wiring layers 108a through 108c and vias 110a through 110c. More specifically, the energy generating element 150 is connected to the third via 110c while the first wiring layer 108a is connected to the p-type impurity region 103, which is the source/drain region of the transistor 120, by way of a fourth via 110d that is formed in the second heat accumulation layer 105. Additionally, an electrode 130 is also electrically connected to the transistor 120 by way of the wiring layers 108a and 108b and the vias 110a and 110b. 
Thus, in the liquid ejection head 140 illustrated in FIG. 6, the wiring that is connected to the energy generating element 150 includes the vias 110a through 110c that are respectively formed in the layer insulating films 106, 107a and 107b. With this arrangement, a large current capacity is secured for the wiring that is connected to the energy generating element 150 and the energy generating element 150 represents improved energy efficiency.